A laser diode (semiconductor laser) is a diode in which a forward current is applied to a pn junction and light is emitted by stimulated emission caused by recombination of injected electrons and holes. The laser diode has been widely used mainly for the information industry including the reading and writing of optical disks such as CD and MD, the laser printer and medical and measurement equipment.
There are several types of laser diodes such as a single-beam laser diode (single-beam semiconductor laser) and an array laser diode (array semiconductor laser). The single-beam laser diode is a laser diode device having only one light-emitting portion, and the array laser diode is a laser diode device having plural light-emitting portions. Since the array laser diode can easily increase the number of scanning beams compared with the single-beam laser diode, it is suitable for the laser printer used for high-speed printing. Furthermore, the array laser diode is also called as a multi-beam laser diode.
In recent years, in order to improve the dissipation of the heat generated in a light-emitting portion in a laser diode, a junction-down method in which a main surface side of a laser diode chip having the light-emitting portion is directed to a submount side and bonded to the submount by using solder or the like has been generally used as a bonding method.
Japanese Patent Application Laid-Open Publication No. 2008-42131 (Patent Document 1) discloses a technology for preventing a layer damaged by dry etching from being left on a ridge-shaped waveguide structure positioned in an upper part of a light-emitting portion in a waveguide semiconductor laser. Specifically, a spacer layer and a damage receptive layer are formed on a contact layer in an upper part of a ridge-shaped waveguide structure to make the two layers absorb the damage caused when removing a passivation film in an upper part of the ridge-shaped waveguide structure by dry etching, and then, the spacer layer and the damage receptive layer are selectively removed by wet etching. In this manner, the spacer layer and the damage receptive layer damaged by dry etching are removed, so that the deterioration of the device can be prevented.
Furthermore, in the above-described Patent Document 1, the upper surface of the ridge-shaped waveguide structure becomes lower in height than the upper surface of the damage receptive layer by the spacer layer and the damage receptive layer formed for the purpose of preventing the ridge-shaped waveguide structure from being damaged by dry etching, so that the ridge-shaped waveguide structure is protected from being hurt in the assembly process of the device.
Japanese Patent Application Laid-Open Publication No. 2008-277471 (Patent Document 2) discloses a technology in which, when an array semiconductor laser is assembled while directing a bonding surface downward, only a specific portion of a laser chip is soldered and a stress absorbing portion is formed below a bonding portion, thereby making it difficult to transmit the stress generated due to the difference in thermal expansion coefficient between the laser chip and the submount to the laser chip.